The governors of the border states of New Mexico, Texas and Arizona -- all Republicans -- expressed their support. But the office of the California governor, a Democrat, did not indicate to CNN whether the governor would back deploying Guard troops.

In announcing the plan Wednesday, Homeland Security Secretary Kirstjen Nielsen said the administration intended to work "in conjunction with" border state governors. The Trump administration has not approached the plan as a national effort, and said it has reached out only to governors from Southwest border states about deployment.

Mike Lonergan, a spokesman for New Mexico Gov. Susana Martinez, told CNN the governor "​appreciates the administration's efforts to bring states to the table as they go about taking steps to better secure our border." Lonergan added that the governor "fully" supports the men and women of the New Mexico National Guard "in any mission -- state or federal at home or abroad."

In a news release Wednesday, Texas Gov. Greg Abbott said the Trump administration directive "reinforces Texas' longstanding commitment to secure our southern border and uphold the Rule of Law, and I welcome the support."

Lt. Col. Travis Walters, Texas Military Department state public affairs officer, told CNN the state is "awaiting additional guidance from the Department of Defense and President regarding the border."

"At this point we are in the very early planning stages," he said.

Nielsen said via Twitter on Thursday that she had "a productive conversation with the southwest border governors."

Arizona's Gov. Doug Ducey responded on Twitter that his state "welcomes this enhanced security," and that he appreciated the opportunity to discuss the plan with Nielsen as well as Abbott, Martinez and California's Gov. Jerry Brown.

Brown's office confirmed to CNN that the governor participated in Thursday's call with the Department of Homeland Security but said it had nothing to add beyond a statement from Lt. Col. Tom Keegan, a spokesman for the California Army National Guard, released Wednesday.

"This request -- as with others we've received from the Department of Homeland Security, including those for additional staffing in 2006 and 2010 -- will be promptly reviewed to determine how best we can assist our federal partners," Keegan said in the statement. "We look forward to more detail, including funding, duration and end state."

Some governors from other states indicated they would resist any attempt to send National Guard troops from their states, if asked by the administration.

Mary-Sarah Kinner, the communications director for Nevada Republican Gov. Brian Sandoval, said in a statement to CNN that the governor "does not think this would be an appropriate use of the Nevada National Guard," adding that the Trump administration has "not been in touch with" the governor's office about the deployment plan.

Oregon Democratic Gov. Kate Brown tweeted Wednesday that if the President asked her to deploy guard troops to the border she would reject the request. "As Commander of Oregon's Guard, I'm deeply troubled by Trump's plan to militarize our border," she said.

The offices of other governors indicated their support.

Arkansas Republican Gov. Asa Hutchison tweeted: "I just spoke with @SecNielsen of @DHSgov. I informed the Trump Administration that the Arkansas National Guard will support @POTUS's effort to increase border security."

"We have done this before, and the technical support of the @arkansasguard will add to our nation's security at an important time. I appreciate General Berry and ANG soldiers for their service."

Hutchinson spokesman J.R. Davis told CNN there have been no formal requests to deploy.

The office of Alabama Republican Gov. Kay Ivey said in a statement to CNN that if the President asks for the state's help, the governor "will work with Adjutant General of the Alabama National Guard to see what resources are available without impeding missions here at home, and then make a determination."

Representatives for some governors indicated that they had not heard from the administration with respect to the plan.

A spokesperson for Florida Republican Gov. Rick Scott said "the Florida National Guard has not received any requests from the federal government."

Shelby Wieman, spokeswoman for Colorado Democratic Gov. John Hickenlooper, said, "We have not been contacted. We've not been asked to deploy."

CNN reported Wednesday that key aspects of the plan had not yet been finalized, including how many troops would be sent and the cost of the deployment.

The memorandum that Trump signed late Wednesday says that "the security of the United States is imperiled by a drastic surge of illegal activity on the southern border" and "the situation at the border has now reached a point of crisis."

In a tweet Thursday morning, the President claimed that thanks to the actions of his administration, border crossings have fallen to a 46-year low but said the level was still unacceptable.

In December 2017, the acting deputy commissioner of Customs and Border Protection, Ronald Vitiello, touted "historic low numbers this year" in an announcement of end-of-year immigration enforcement statistics, including "an almost 30 percent decline in apprehensions" for that fiscal year.

More recently, however, there has been a rise in the number of attempted illegal border crossings into the US from Mexico.